3377 ex2

what does chsh do?

changes your login shell

Makefile definition

A GNU utility that determines which pieces of a large program need to be compiled or recompiled; issues commands to compile and link them in an automated fashion

Variables in a Makefile

PROG = textr

CC = g++

CPPFLAGS = -g –Wall –I/usr/class/cs193d/textrInc

LDFLAGS = -L/usr/class/cs193/lib –lCoolFns

OBJS = main.o blurb.o database.o

Targets in a Makefile

$(PROG) : $(OBJS)

$(CC) $(LDFLAGS) -o $(PROG) $(OBJS)

main.o :

$(CC) $(CPPFLAGS) -c main.cpp

blurb.o : blurb.h

$(CC) $(CPPFLAGS) -c blurb.cpp

database.o : database.h

$(CC) $(CPPFLAGS) -c database.cpp

clean:

rm -f core $(PROG) $(OBJS)

Pre-req in a Makefile

$(PROG) : $(OBJS)

$(CC) $(LDFLAGS) -o $(PROG) $(OBJS)

main.o :

$(CC) $(CPPFLAGS) -c main.cpp

blurb.o : blurb.h

$(CC) $(CPPFLAGS) -c blurb.cpp

database.o : database.h

$(CC) $(CPPFLAGS) -c database.cpp

clean:

rm -f core $(PROG) $(OBJS)

Rules in a Makefile

$(PROG) : $(OBJS)

$(CC) $(LDFLAGS) -o $(PROG) $(OBJS)

main.o :

$(CC) $(CPPFLAGS) -c main.cpp

blurb.o : blurb.h

$(CC) $(CPPFLAGS) -c blurb.cpp

database.o : database.h

$(CC) $(CPPFLAGS) -c database.cpp

clean:

rm -f core $(PROG) $(OBJS)

What would be in a textr in a makefile

included files and libraries

echo -n “Hello”

print “Hello” without a newline

echo -e “Hello\nWorld”

print “Hello”

“World”

$echo “Hi, \n this is a test.”

Hi, \n this is a test.

echo -e "Hello\aWorld"

will trigger an alert sound if enabled

echo -e "Hello\bWorld"

“HellWorld”

echo -e "Hello\cWorld"

“Hello”

echo -e "Hello\fWorld"

“Hello” followed by form feed

echo -e "Hello\rWorld"

“World”

echo -e "Hello\tWorld"

“Hello World”

echo -e "Hello\vWorld"

Hello

World

name="Fatima"

echo 'Hello, $name'

“Hello, $name”

what does set do

will see all shell variables and functions

unset

removes variables or function from the current shell enviorment

shell variable rules

must begin with a lowercase or uppercase letter and not a digit, no spaces on either side of the equal sign ex. age=32

PS1

set to the string used as your prompt sign

PS2

set to the prompt sign that is displayed whenever you press RETURN

CD

set to absolute pathname

SHELL

set to the full pathname of your login shell

TERM

sets your terminal type

TZ

sets the time zone that you are in

echo "Today is `date`"

Today is Mon Oct 30 10:45:00 UTC 2024

what does ; do

allows multiple commands on the same line

(ls -C ; date ; pwd) > outfile

three commands in sequence, grouped together, with the output redirected to a file

what does & do

sends command to run in the background

pipe operator |

uses the output of one command as the input to another command

-n

number all output lines

-A

show all charcters inclufing non-printing charcters ex. ^I as tabs

-b

number only non-empty output lines

cut -c 1-5 data.txt

print the first 5 characters from each line

cut -d ',' -f 1,3 data.csv

print the first and third columsns using , as delimiter

echo “Hi, `sleep 10` Thanks for waiting”

will print hi and the thanks for wiating after 10s

wc command

counting command takes file as an argument

wc -l example.txt

num example.txt

ps -a

displays the status of all the active process, not just users

ps -f

displays full list of information including the full command line

kill command

terminates process

tee command

ls _C | tee dir.list

displays the current directory file names and also saves the output in dir.list

grep command

search for a specified pattern in a file or list of files

grep UNIX myfile

finds the lines that contain the word UNIX in myfile

grep -e "apple" -e "banana" fruits.txt

apple

banana

grep -i "apple" fruits.txt

Apple; makes the search regardless of upper or lower

grep -l "apple" fruits.txt vegetables.txt

fruits.txt; the file that the word is in

grep -n "apple" fruits.txt

1:apple

grep -v "apple" fruits.txt

banana

cherry

words that are not apple

sort -b data.txt

will ignore leading blanks when sorting

sort -d data.txt

sort with dictionary order; upper and lower case matter, upper first

sort -f data.txt

will sort ignoring upper and lower case

sort -n numbers.txt

sort numbers in a file

sort data.txt -o sorted_data.txt

sort and save th output in data.txt

sort -r data.txt

sort in reverse order

what is shell script

a command language - interpreted not compiled

sh command

run a script

$0

contains the name of the script

$1, $2…

contains the first through x command line parameters

$#

conatins the number of command line parameters

$@

contains all command line parameters: $` $2…

$?

conatins the exit status of the last command

$*

contains all command line parameres

$$

conatins PID number of the executing process

what does the read command do

used to read a line of input from standard input; accept input from user

exit n

exit

echo $?

print exit status of the last executed command

num1 -eqnum2

is num1 equal to num2

num1 -nenum2

is num1 not equal to num2

num1 -gtnum2

is num1 greater than num2

num1 -genum2

is num1 greater than or equal to num2

num1 - ltnum2

is number1 less than num2

num1 -lenum2

is num1 less than or equal to num2

string1 = string2

does string1 match string2

string1 != string2

does string1 not match string2

-n string

does string conatin characters (nonzero length)

-z string

is string an empty string(zero length)

-r filename

does filename exist and is it readable

-w filename

does filename exist and is it writable

-s filename

does filname exist and does it have a nonzero length

-f filename

does filename exist, but is it not a directory file

-d filename

does filename exist and is it a directory file

${variable: -string}

the valua of variable if it is set and not empty; otherwise the valus of string

${variable: +string}

the value of string if variable is set and not empty; otherwise variable is set to the value of string

${variable: =string}

the value of variable is it is set and not empty; otherwise variable is set to the value of string

${variable: ?string}

the value of variable if it is set and not empty; otherwise print the value of string and exit

expr 10 \* 2

20

expr 10 \% 3

1

x=`expr $x + 1`

adds 1 to x

can you use expr and let interchangibly

yes

for format

for variable

in list-of-values

do

• commands

• last command

done

while format

while

do

commands

last command

done

until

until

do

commands

last

done

-similar to while but will continue executing as along as the condition is false

alias command

for shortening the names of frequently used commands or changing command names

history command

keeps a list of all the commands you enter during the session

how to restart the history

remove the .sh_history

history 104

start from the command number 104